Liquid crystalline polymer (LCP) films have properties that are very desirable, such as excellent chemical resistance, high strength, and excellent gas barrier properties. However, these same films have certain undesirable properties. They often have poor transverse mechanical properties (i.e. they are strong in the machine direction, but tear easily in the direction transverse to the machine direction). It is also difficult to write or print on the films. LCP films are more expensive than conventional polymer films, such as polyester films.
It would be desirable to make multilayer films having LCP film bonded to one or more other films to obtain a film having the best properties of all of the various layers, such as a multilayer film having the good gas barrier properties of an LCP and the relatively low cost of a conventional polymer.
However, LCP films do not bond well to each other or to other films by use of an adhesive. Their surfaces do not in general adhere to adhesives. There are thus very few examples of multilayer films containing one or more LCP layers. Multilayer films in which LCP's and polypropylene are bound together are also rarely mentioned. One example can be found in Japanese Patent Application No. 02-253,950, published in 1990, where a poly(butylene terephthalate) film layer is bound to VECTRA.RTM. A 900 LCP film using a glycidyl-modified ethylene vinyl acetate adhesive. The other side of the VECTRA film is bound to polypropylene film by using two adhesive layers, a glycidyl-modified ethylene vinyl acetate layer in contact with the LCP and an ethyl acrylate-ethylene-maleic anhydride copolymer in contact with the polypropylene. Japanese Patent publications 02-253,951 (1990) and 04-135,750 (1992) use similar adhesives for binding an LCP to poly(butylene terephthalate) and polypropylene. The latter of these patent applications also uses a saponified ethylene-vinyl acetate copolymer as an adhesive. Other publications that discuss multilayer films comprising an LCP barrier layer include Japanese Patent Publication 02-307,751 (1990), PCT Patent Publication WO 95/23180, and European Patent Application No. 763,423.